Memory circuits have continued to have more and more bits of storage primarily due to the continued scaling of the processes used in making the memory circuits. As this has developed more and more bits per access has become common as has the practice of dividing the memory circuit into more and more blocks. For example a memory of 1 MB (about 8 million bits) may be divided into 64 blocks and each block having 8 subarrays and each access being for 512 bits of data. As the scaling has developed, not just have the dimensions of the smallest feature sizes gotten smaller, the power supply voltages have also gotten smaller. A continuing problem in all of these memories is power supply voltage drop over the memory so that the actual voltage being provided is lower than the power supply voltage. A number of schemes have been developed such as having multiple layers of interconnect over the memory in which the power supply lines are interleaved with signal lines. Another technique that has been proposed is to stagger the accessing of the various memory blocks to reduce the peak IR (current times resistance) drop. An IR drop is a reduction in voltage that occurs when current flows. A higher current causes a higher IR drop and thus more voltage reduction. One of the primary reasons for the transition from aluminum to copper interconnect is to have lower resistance interconnect and thus less IR drop as well as reduced RC (resistance time capacitance) constants.
Thus, at present there is still a need for further improvement in the effects of IR drop for memory circuits.